1. Field of the Invention
This invention relates to an image recording method and apparatus in which a latent image is formed on a photo-sensitive material and is then thermally developed with the photo-sensitive material held between a heating drum and an endless belt.
2. Background Art
One example of an image recording material utilizing micro-capsules containing photo-sensitive compound has been disclosed, for instance, in Japanese Patent Application (OPI) No. 179836/1982 (the term "OPI" as used herein means an "unexamined published application"). The image recording material comprises a support and synthetic macromolecular resin wall capsules which contain vinyl compound, photo-polymerization initiator and coloring agent precursor which are carried on the support. This photo-sensitive material is optically exposed to form a latent image thereon so that the polymerizing compound is hardened according to the latent image thus formed. The latent image is developed under pressure.
In an image recording method using the image recording material, the image recording material is optically exposed to form a latent image thereon to harden the microcapsules according to the image. The microcapsules not so hardened are broken by application of pressure to the image recording material so that the coloring agent precursor is discharged to obtain a colored image. The method is advantageous in that an image of high picture quality can be readily obtained without wet processing. However, the image recording material is disadvantageous in that it is much lower in photo-sensitivity than an image recording material using silver halides.
A novel image recording material which has a higher photo-sensitivity than the above-described one and provides a high quality image by simple dry processing has been disclosed in Japanese Patent Application (OPI) No. 275742/1986 filed by the present Applicant.
An image recording method using that image recording material, namely, a photo-sensitive pressure sensitive thermal developing material, has been disclosed in Japanese Patent Application (OPI) No. 278849/1986 filed by the present Applicant. In this method, a latent image first is formed on the image recording material by optical exposure and then thermally developed so that the polymerizing compound in the region of the latent image is polymerized to produce a macromolecular compound to thereby harden the microcapsules. Thereafter, the image recording material is piled on an image receiving material having an image receiving layer onto which color image forming material can be transferred. The thus piled image recording material and image receiving material are pressed together so that at least some of the microcapsules in the region where not latent image is formed are broken so that the color image forming material is transferred onto the image receiving material to form the image of the latter.
An image recording apparatus for practicing the above-described image recording method has been disclosed by Japanese Patent Application No. 5189/1986 filed by the present Applicant. This method comprises the steps of forming a latent image on the photo-sensitive material by optical exposure, thermally developing the latent image thus formed, piling the photo-sensitive material on the image receiving material, and pressing together the thus piled photo-sensitive material and the image receiving material so that the image thus developed is transferred onto the image receiving material.
A thermal developing method and an apparatus for practicing the above methods have have been proposed in the art to perform the above-described thermal developing operation. In the method and apparatus, a heating drum having an interior heater and an endless belt laid on it are turned so that the latent image is thermally developed with the photo-sensitive material held between the heating drum and the needless belt. Thereafter, the photo-sensitive material is delivered to a sheet piling section.
The above-described method and apparatus are advantageous in that, since the heating drum and the endless belt hold the photo-sensitive material while turning at the same time, the photo-sensitive material is stably conveyed. However, they are disadvantageous in the following points.
While the image recording operation is suspended, i.e., while the driving of the heating drum and the endless belt is suspended, the heating drum is maintained at a predetermined temperature. Therefore, the part of the endless belt which is in contact with the surface of the hating drum is also held at the predetermined temperature, whereas the temperature of the remaining part of the endless belt which is not in contact with the surface of the heating drum gradually decreases.
When, under this condition, the heating drum and the endless belt are turned for thermally developing the latent image on the photo-sensitive material, the low temperature part of the endless belt comes to contact the surface of the heating drum to thereby cool it. As a result, the drum surface temperature is decreased about 6.degree. C. form the desired temperature. If, under this condition, the thermal developing operation is carried out with the photo-sensitive material held between the heating drum and the endless belt, then since the developing temperature of the photo-sensitive material tolerates only a .+-.2.degree. C. temperature variation, the photo-sensitive material is not uniformly heated. That is, the developing of the part of the photo-sensitive material which is not sufficiently heated is delayed, as a result of which the density of the image at that part is higher than originally it was intended to be. Thus, the resultant image is not uniform in density.
Another novel image recording material has been disclosed by Japanese Patent Application No. 117089/1985 filed by the present Applicant, to eliminate the above-described difficulty accompanying the conventional image recording material. The novel image recording material is high in photo-sensitivity and can provide an image of high picture quality by simple dry processing. The image recording material is formed by coating a support at least with a photo-sensitive silver halide, reducing agent, polymerizing compound and color image forming material, and among these materials, at least the polymerizing compound and the color image forming material are, in combination, sealed in microcapsules.
An image recording method using that image recording material has been disclosed in Japanese Patent Application No. 121284/1985 filed by the present Applicant. In this method, the image recording material is optically exposed to form a latent image thereon and is subjected to thermal developing so that, in the region of the latent image, the polymerizing compound is polymerized to produce macromolecular compound to harden the microcapsules. Under this condition, the image recording material thus processed is piled on an image receiving material having an image receiving layer. The image recording material and the image receiving material thus piled on one another are pressed together so that, in the region where no latent image is formed, at least some of the microcapsules are broken to transfer the color image forming material onto the image receiving material thereby to obtain the visible image thereon.
A further problem is that in the case where the image recording operation is not started yet and the heating drum and the endless belt are not yet turned, but the heating drum is heated by the heater so that the drum surface temperature is maintained constant, the temperature of the contact part of the endless belt with the heating drum rises more quickly than that of the non-contact part of the endless belt. That is, the endless belt is not uniformly heated. As the heating drum and the endless belt are turned, the low temperature part of the endless belt contacts the drum surface to cool down the drum. The endless belt is of heat-resisting rubber, and it is relatively large in thickness so as to be durable against rotation, as a result of which the endless belt has a large thermal capacity. Accordingly, the quantity of heat which the endless belt takes from the heating drum is so large that the drum surface temperature becomes lower by about 6.degree. C. than the desired value. If, under this condition, the photo-sensitive material is subjected to thermal developing while being held between the heating drum and the endless belt, the photos-sensitive material is not uniformly heated because the tolerance and developing temperature of the photosensitive material is only which a range of .+-.2.degree. C. As a result, the part of the photo-sensitive material where the quantity of heat for developing is inadequate is insufficiently developed. Therefore, the image developed on the photo-sensitive material is higher in density than that developed on a photo-sensitive material at the specified temperature. That is, the resultant image is not uniform in density.
A photo-sensitive material of the type in which a photo-sensitive material including silver halide is optically subjected to thermal developing while, in association with the thermal developing, the polymerizing compound is hardened, and thereafter a visible image is obtained through pressurization, has been disclosed by Japanese Patent Application No. 121284/1985 filed by the present Applicant. With this type of photo-sensitive material, after the thermal developing operation, color image forming material is transferred onto an image receiving material having an image receiving layer. The photo-sensitive material is formed by coating a support with at least a photo-sensitive silver halide, a reducing agent, a polymerizing compound and a color image forming material. Among these materials, at least the polymerizing compound and the color image forming material are, in combination, sealed in microcapsules.
When, in the thermal developing method and apparatus, the heating drum is heated by the heater under the condition that the heating drum and the endless belt are stopped during the warm-up period with the power switch turned on, the part of the endless belt which is in contact with the heating drum is quickly increased in temperature, while the temperature of the remaining part of the endless belt which is not in contact with the heating drum rises slowly. That is, the temperature of the endless belt is not uniformly increased. After the temperature of the heating drum has reached a predetermined value, the drum surface temperature is controlled to a certain value, whereas the part of the endless belt which is not in contact with the drum remains at a low temperature. When, under this condition, the heating drum and the endless belt are driven for developing the photo-sensitive material, the low temperature part of the endless belt contacts the drum surface to cool down the drum. For instance, the drum surface temperature becomes lower by about 6.degree. C. than a predetermined value at which it should be maintained. As a result, the photo-sensitive material is not uniformly heated. Since the tolerance of the developing temperature of the photo-sensitive material is of the order of .+-.2.degree. C., the resultant image is foggy in the part of the photo-sensitive material which has not been sufficiently heated for developing and its color density is higher than a predetermined value. That is, the image is not uniform in density.